High Speed Flight + contamination Flashcards
What is the equation for local speed of sound
LSS = 39squarerootk
What is the equation to work out the Mach number
Mach number = TAS / LSS
In subsonic flight describe the Mach. Numbers
All local Mach numbers are below 1
For low subsonic Mfs = <0.4
For high subsonic Mfs = >0.4
Describe transonic Mach numbers
Somewhere
Ml <1
Ml = 1
Ml >1
Somewhere in transonic region Mfs = 1
Describe supersonic Mach numbers
All local Mach numbers >1
What is Mcrit
The free steam Mach number which somewhere on your aircraft you have a local flow of Mach 1
What is Mdet
Mach detachment speed
Measures as free stream
Where do normal shockwaves occur
In the transonic region
Can air flow normally through a normal shockwave
Yeh
What speed is the airflow infront of the normal shockwave
Supersonic
What speed is the airflow behind the normal shockwave
Subsonic
If the air infront of the normal shockwave is 10% above Mach 1 what is the air behind the shockwave like
10% below Mach 1
How thick is the normal shockwave
0.0025mm
What is the most violent shockwave
Normal shockwave
What shockwave creates the most drag
Normal shockwave
What does a shockwave do to temperature and density
Temperature increases (energy comes from total pressure decrease)
When do oblique shockwaves occur
At a higher speed than normal shockwaves
If the speed of the airflow is above Mach 1 infront of the oblique shockwave what speed it is behind
Above Mach 1 but slower
Does the oblique shockwave change direction of the airflow
Yes it does
What creates a bow wave
Normal shockwave
+
Oblique shockwave
What happens to the bow wave as speed increases
Stagnation point (which creates the normal wave) decreases and eventually the bow wave attaches to leading edge creating just a oblique wave
At what speed does the bow wave attach or detach from the leading edge
Mdet
What shockwave do we feel / creates the sonic boom we hear
Oblique shockwaves
How does speed affect the oblique shockwave
Faster we go the more pushed back they become
How does speed affect the Mach cone
Faster you go the smaller the Mach cone around aircraft
What is the Mach cone angle
Angle between flight path and the oblique shockwaves
What is the equation for the Mach cone angle
Sin angle= LSS/TAS
Or
= 1/Mach n
What is the expansion wave
NOT A SHOCKWAVE
Air curving round a surface
Speed or air flow in an expansion increase
Temp decreases
Density decreases
Pressure / energy the same
What happens to Mach number when you go into warmer air
Constant Mach number
Temp ^
Density down
What is chicken tikka masala
In tropopause = chicken. Tikkamasala
In isotherm = chicken masala tika
What happens to AOA as you climb at high speed on constant Mach
Increases (small increase)
What happens to flight path angle if you’re climbing at high speed on a constant Mach
Decreases
What happens to pitch as you’re climbing on a constant Mach at high speed
Decreases
What happens to AOA as you’re climbing on a constant CAS at high speed
Remains constant
What happens to flight path angle as you climb at a contact CAS
Decreases
What happens to pitch at you climb at a content CAS
Decreases
What happens to AOA as you descent on a constant Mach
Decreases
What happens to flight path angle as you descend on a constant Mach
Increases
What happens to pitch angle as you descend on a constant Mach
Decreases
What happens to AOA
Flight path angle
And pitch angle when descending on a constant CAS
Remain constant
What is Mcrit
The free stream Mach number at which somewhere on the aircraft reaches Mach 1
Assuming load factor of 1
How does a thick wing affect Mcrit
Lower Mcrit
What happens above Mcrit
A normal shock wave is formed
As you increase speed up to what point does the cp keep moving rearwards
Just before Mach drag divergence
What happens when separation for normal shockwaves occurs at the trailing edge for both upper and lower normal shockwaves
Most drag
What happens when normal shockwave transforms into an oblique wave
Centre of pressure shoots back to 50%
What happens at Mach 1 Mfs
Normal shockwaves attach to trailing edge and also a bow wave forms
Life of a shockwave
See notes in jotted = can’t type it well
Describe the pressure distribution when there is oblique waves at the trailing edge and a bow wave at the leading edge
Uniform pressure distribution over the wing
When is a aircraft super sonic
After Mdet
When is the Mach drag divergence
Just beyond Clmax
When is the worst Cl/Cd ratio for high speed flight
Mfs 1
What happens when the cp shoots aft in high speed flight
Pitch forward = Mach tuck
Aircraft needs a Mach trimmer
= needs all moving tailplane
What happens to stick force gradient after Mcrit
Stick force gradient becomes neutral (doesn’t get harder to move with height)
After even more speed increase eventually becomes negative
What is the aerodynamic ceiling
At this height any increase / decrease in speed results in stall or shock stall
What is the buffer margin
A range of speeds below the ceiling to ensure u don’t stall and to allow for turbulence / disturbance
What does aerodynamic ceiling reduce with
Anything that increases stall speed
What is the manoeuvre ceiling
Aerodynamic ceiling adjusted for the ability to manoeuvre
How does thickness to chord ratio affect Mcrit number
High thickness to chord ratio = lower Mcrit number
What is a super critical wing
Large radius leading edge
Flatter upper surface
Both negatively and positively cambered aerofoil
Better for high speed flight than a normal wing of similar thickness to chord ratio
How does sweep back wings affect Mcrit
Increases effective chord length
Reduces thickness to chord ratio
Increases Mcrit
What can you put infront of the usually places for separation to occur due to shockwaves
Vortex generators
What is wave dependant on
Surface area (cross sectional area)
How can you reduce wave drag
Area ruling
Intending the fuselage for wings to reduce cross sectional area
What are the disadvantages of s supercritical aerofoil
can produce rapid and unpredictable movement of the separation point
Poor low speed handling
Large nose down pitching moment because majority of lift occurs in the rear 30% of wing
Isn’t practical wing shape for root which makes installation of trailing edge devices difficult
What happens to Mcrit when you sweep back a wing
Effective chord longer = reduces thickness - chord ratio = increases Mcrit
What is airframe contamination
Anything that is going to change the surface of the aircraft
Where is frost most likely to form on a aircraft
Under the wing due to cool fuel
Brush off or de-ice
What airspeed does frost not tend to form above
250knots
Where does snow form inflight usually
Stagnation points
Leading edges
What airspeed does rime ice not tend to form over
250 knots
How can you get rid of rime ice
Warming leading edge
Or
Inflatable boots (however they need to let ice build up first)
What aircraft is most at risk from clear ice
Turbo props as they usually fly in the altitudes associated with it
What effect does contamination have on drag
Skin friction drag increase
Increased weight = induced drag increase
What thickness aerofoil is worst for icing
Thin aerofoil
What aircraft surface is most susceptible to icing
Tailplane because it’s a thin aerofoil
What phase of flight is tailplane icing the biggest risk
Approach
= slow speeds, large downwash
What effect could flaps have on the tailplane if it is iced
Flaps down = greater Downwash = greater AOA on tailplane = if iced could stall
How to recover from a tailplane stall due to flaps in icing conditions
Return to previous flap setting
What anti icing is left on permanently
Pitots
Pilot window (more stronger protection against bird strikes if warm)
What is deformation
Damage twisting buckling
Changing shape
What is degradation
Surface worn away over time
Solved by repainting
Eqn for local speed of sound
39 squareroot temp in kelvin
How to calculate the Mach cone angle
Sinangle = 1/Mach number
Or
Sinangle = LSS/TAS
